At the close of the 18th century, he [Von Zach] organised the “Celestial Police”, a group of twenty-four astronomers, to prepare for a systematic search for the “missing planet”
predicted by the Titius-Bode law between Mars and Jupiter. Ceres was discovered by accident just as the search was getting underway.

Using predictions made of the position of Ceres by Carl Friedrich Gauss, on 31 December 1801/1 January 1802, Zach (and, independently one night later, Heinrich Wilhelm
Matthias Olbers) recovered Ceres after it was lost during its passage behind the Sun.

After the death of the duke in 1804, Zach accompanied the duke’s widow on her travels in the south of Europe, and the two settled in Genoa in 1815 where he directed
the Capodimonte Observatory. He moved back to Paris in 1827 and died there in 1832.